Methods for scanning an examination object by way of a CT system are generally known. In this case circular scans, sequential circular scans with advance, or spiral scans are used, for example. With the scans, absorption data of the examination object are recorded from different recording angles with the aid of at least one X-ray source and at least one oppositely disposed detector, and the thus collected absorption data or projections are computed by means of appropriate reconstruction methods into sectional images (slices) through the examination object.
A method referred to as filtered back-projection (FBP) is currently employed as the standard method for reconstructing computed tomography images from X-ray CT data sets of a computed tomography device (CT scanner), i.e. from the acquired projections. Following the data acquisition a step referred to as “rebinning” is performed in which the data generated by the beam widening out in the shape of fan from the source are re-ordered in such a way that they are present in a form as though the detector were struck by X-rays converging in parallel onto the detector. The data are then transformed into the frequency domain. Filtering takes place in the frequency domain and subsequently the filtered data are back-transformed. With the aid of the thus re-sorted and filtered data a back-projection is then performed onto the individual voxels within the volume of interest.
A disadvantage of these generally known calculation methods is that in the case of a moved or moving examination object, or an at least partially moved examination object, motion unsharpness can occur in the image, since during the time of a scanning operation to capture the data required for an image a displacement of the examination object or a part of the examination object can be present, with the result that not all the data that lead to an image reflect a spatially identical situation of the examination object. This motion unsharpness problem arises in a particularly extreme form during the performance of cardio CT examinations of a patient in which a strong motion unsharpness can occur in the cardiac region due to the cardiac movement or in the case of examinations in which relatively quick changes in the examination object are to be measured.